Electricians and others often need to determine the configuration of electrical plugs and wires in electrical systems such as determining the phase or phases of a plug and the configuration of a fuse box. For example, electricians sometimes need to determine which phases the fuses are associated with and sometimes which particular fuse that is connected to a particular electrical plug. The currently used methods are not only quite cumbersome but also dangerous particularly if it is not possible to turn off the electrical system during the testing procedure. For example, when the electrical system cannot be shut off, some electricians short-circuit the plugs to trigger the fuses to determine which fuse is connected to which plug. This method can create fires and injuries to the electrician. It may also damage the devices that are connected to the electrical system. The currently available testing devices are sensitive to how the testing device is connected to the electrical plug. The voltage phase and/or the reference phase must be in the right place to make the tester show the correct result. The displayed result of the phase configuration often depends on how the testing device is turned when it was plugged in. If the testing device is turned upside down a different result is shown compared to the situation when the upside is turn upwardly. It may not be able to detect the situation when one of the wires carries a current but there is no ground or zero-reference component. It is also difficult to test ground fault devices that are used to detect ground faults to make sure the devices are triggered within a certain permitted time period. Despite many efforts, the currently available devices and methods are not satisfactory. There is a need for a reliable and effective device and method that may be used to accurately and safely determine the configuration of electrical systems while the system is in full operation.